Australian Prime Minister Tony Abbott yesterday said he would not succumb to "moral blackmail" over a detention centre on Papua New Guinea, as graphic witness accounts of recent violence told of "blood everywhere".

Unrest at the Manus Island camp this week left an Iranian man dead and more than 70 injured as tensions flared among inmates about their fate under Australia's harsh asylum-seeker policies.

Canberra has sent the head of its military-run Operation Sovereign Borders, Angus Campbell, to the island to assess security and work out what happened.

Despite the violence and demands from refugee advocates that the facility, condemned by the UN, should be closed, Abbott said he would not step back from his strong border-protection policies.

"We will not succumb to pressure, to moral blackmail," he said. "We will ensure these camps are run fairly, if necessary, firmly."

Manus Island is one of two remote Pacific camps used by Canberra in its punitive offshore detention policy, with the other on Nauru.

Under the scheme, aimed at deterring people-smugglers, any asylum-seeker arriving by boat or intercepted at sea is transferred to Manus or Nauru for processing and permanent resettlement outside Australia.

There are conflicting accounts of what sparked the riot on Monday, with claims that islanders, unhappy about the camp and armed with machetes, broke in. Others say the asylum-seekers tried to escape, while security guards have also been blamed.

A man who said he witnessed the violence claimed PNG guards employed by the G4S security company running the centre became angry when asylum-seekers shouted insults about their country and families.

He said the guards beat detainees with sticks, iron bars and rubber hoses.

"When they pulled them outside they started beating them with the sticks... some of them with sticks and some of them with all these hose, rubber hose and pipes," he told ABC radio.

An interpreter employed by the Australian Immigration Department said asylum-seekers used plastic chairs as shields when G4S guards attacked them with machetes, knives and rocks.

"Definitely, 100 per cent, I stand by the statement that the local people, including some employed by G4S, they were the ones who caused this drama," Azita Bokan told Fairfax Media after flying out of Manus Island on Wednesday.

"There was blood everywhere. The number injured was horrific. People with massive head injuries, at least one with a slashed throat."

Her comments back what refugee advocates have said.

G4S said "we take these allegations seriously and we as a company do not tolerate violent or abusive behaviour from our staff".

But it added: "Our personnel on duty during the disturbances acted with courage, strength and determination to protect those in our care."